The invention relates to an electric lamp comprising:
a lamp envelope, PA1 a light source within the lamp envelope which is energizeable for emitting light, PA1 an electrically conductive lead extending from the light source within the lamp envelope to the exterior of the envelope, and PA1 a lamp cap having (i) an electrically insulative portion and (ii) a lamp cap contact to which the electrically conductive lead is clamped. PA1 the lamp cap contact comprises (i) a contact portion for contacting a corresponding contact in a socket and (ii) a rigid shank extending from the contact portion; and PA1 the insulative portion has a bore wall defining a clamping bore for receiving the shank, the bore being sized and the insulative portion surrounding said clamping bore having an elasticity selected such that (i) the electric lead is securely clamped between the shank and the bore wall when the shank is inserted into the clamping bore with the contact portion seated against the insulative portion and (ii) the lamp contact is secured in the clamping bore solely by friction between the shank and the bore wall, the shank and the bore wall being free of any snap-type engagements.
Numerous examples of lamps with lamp caps having a contact which clampingly receives a conductive lead are present in the art.
A first group of lamp caps in the prior art discloses a generally planar disk-shaped end contact with various flaps or protrusions to mechanically secure the lead wire. U.S. Pat. No. 2,664,551 shows a lamp cap in which the end contact has a tubular metal extension with four quadrants or flaps. The lead is secured to the tubular extension by folding the four flaps over each other, trapping the center lead wire therebetween. This construction has the disadvantage of a complex shape and a complex assembly with numerous steps. The end cap first must be secured in the insulative material, and then each of the four distinct flaps folded over each other to trap the lead therebetween. Additionally, the folded flaps present a different, if not unfinished, appearance from the smooth, button-shaped appearance provided by traditional soldering techniques. In U.S. Pat. No. 2,736,873, the protrusion is a dome-shaped boss with an aperture through which the lead wire is threaded. The lead is secured in the aperture by swaging the wire and boss with the aid of a rotating die to flatten the end of the wire against the boss and to roll the rim of the aperture against the opposite side to clamp the lead therebetween. JP 58-53655 shows another modification in which the disc shaped end cap has a single flap which is bent over, trapping the lead between opposing edges of the flap and the aperture defined by the flap. The bent over flap does not itself provide sufficient electrical and mechanical contact, as the lead wire is additionally welded to the flap. U.S. Pat. No. 2,732,532 shows yet another construction in which the protrusion in the disc-shaped end contact is in the form of four circumferentially spaced inwardly extending lips. DD PS 221.299 shows still another variation in which the protrusion is a slotted tube which is clamped about the lead wire and cut to length together with the lead wire. The lead wire is then also welded to the tube. Besides the rather complex and costly flap constructions presented by some of the above designs, they have in common that they require at least two assembly steps: the disk must first be secured in the insulative body, and then the protruding flaps, lips etc. must then be mechanically deformed by a tool to trap the lead wire.
U.S. Pat. Nos. 3,629,640 and 3,775,634 show another type of lamp cap construction in which the lead wire is clamped between a protruding boss of the insulative body and a metallic end cap which forms the center contact. In the '634 patent, the insulator body is of a fast firing glass-ceramic body and the end cap is secured to the boss by a force fit, glue or solder. For a force fit, the cap has a tubular portion with an inner diameter slightly smaller than that of the combined diameter of the boss and the lead wire. This construction would require tight tolerances on the inner diameter of the cap because of the rigid nature of the glass-ceramic body and the un-slotted construction of the tubular portion of the metallic end cap, which requires local deformation of the tubular portion about the lead wire to obtain a suitable force fit. In the '640 Patent, the insulator body is glass and the boss has a tapered or profiled shape. The metal end cap must be mechanically worked to deform it onto the tapered or profiled edge of the boss.
U.S. Pat. No. 2,336,529 shows another design in which the lead wire is fixed within a central bore of the insulative body by a metallic plug with "snap action". The plug has a planar disk-shaped portion and a generally cylindrical portion which is split into a plurality of spring-like locking fingers. The fingers have bevelled edges at their free ends for snapping over the shoulder of the insulator body. The spring-like fingers are relatively complicated, rendering the contact plug comparatively expensive to manufacture. Additionally, the plug is only secured to the insulator body by the force exertable by the elongate fingers, so movement of the plug and intermittent electrical contact with the end plug, with resultant arcing, would be expected. The '529 patent also shows an embodiment in which the center contact is a tubular rivet with a flat outer head. Once the lead is passed through the center bore, the rivet is inserted into this bore with the wire between the insulator body and the rivet. The free end of the rivet inside the insulator body is then deformed by an undisclosed tool inserted through the tubular portion from the head end. As with the disc-shaped contacts first discussed, the extra step of mechanically deforming the contact is required, as is trimming of the excess lead wire.
The above-mentioned designs generally concern the fixation of the center lead wire to the center contact. Various forms of clamping are also known in the prior art for the side lead wire. The above-mentioned '529 patent discloses an embodiment in which the insulator body is secured in the threaded shell by rolling of the shell or a snap-fit action with the shell. The side lead wire is secured between the insulator body and the threaded shell. The wire extends in the direction of the shell and the excess wire needs to be trimmed-off. Additionally, it is known from commercially available compact fluorescent lamps to fix the side lead-wire between the threaded metallic shell of the lamp cap and the plastic housing by swaging, pinning, or otherwise deforming the threaded shell onto the plastic housing with the side lead wire therebetween.
Despite the numerous known configurations for lamp caps with a mechanically fixed lead wire, lamp caps in which one or both lead wires is soldered or welded to a metal portion of the shell still predominate on commercially available lamps with threaded lamp caps, such as Edison bases. The solders which have been widely used in the industry contain lead. In addition to its increased expense in recent years, it is desirable to avoid the use of lead-containing materials. Additionally, welding is not always a viable alternative because of the difficulty in achieving reliable contact of both welding electrodes with many lamp cap configurations.
Accordingly, it is the object of the invention to overcome the above-mentioned disadvantages of the prior art lamp caps and to otherwise provide an electric lamp with an improved, solder-free and weld-free construction.